Stair climbing platform apparatus and method

ABSTRACT

A platform wheeled apparatus that incorporates an intelligent wheel configuration for each wheel in which each wheel can dynamically change its radius to negotiate various obstacles. The intelligent wheel has a rotational hub and support disc that carries a series of arcuately spaced extendable, weight bearing radial spoke mechanisms that can be controllably extended and retracted in response to the anticipated terrain surface over which the wheel is to travel. The hub of the intelligent wheel carries a microcontroller for a set of obstacle proximity sensors, force and position sensors and an appropriate electrical power supply for operation of the spokes and control components.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to vehicles and more particularly to aplatform vehicle that can negotiate obstacles such as stairs.

2. Description of Related Art

Today, there are increasingly complex demands for robotic systemsoutside a modern factory floor. One significant problem, at present, isthat wheeled platforms have difficulty navigating over uneven terrain,and traversing obstacles. While significant work has been done onbipedal and multi-legged robots, these systems typically have muchhigher power requirements than wheeled platforms. Wheeled platforms are,perhaps, the most efficient mechanisms for moving across any surface.Legged platforms require power both to move the platform horizontallyacross the surface, and require additional power to both support theplatform and to lift and move the legs themselves. The wheel provides apassive support to the load, negating the need for the power needed tolift the platform. However, wheels are only efficient if the surfaceover which they travel is flat and relatively smooth, and wheels fail ifthere are either vertical obstacles, or significant voids in thesurface. Hence, wheels have shown their worth in carefully engineeredenvironments, and have failed in more complex domains.

Such uneven terrain may include vertical discontinuities, steps, andstairs, and situations where those surfaces are potentially covered witha variety of debris. For instance, if a traditional wheel wereapproaching a curb from the road surface, the curb would present avertical obstacle, over which the wheel would have to climb. Since theonly driving force on the wheel is the forward rotational motion, thegeometry of the wheel and the curb has to translate the forward motioninto upward motion, and thus raise the center of mass of the wheel. Ifthe radius of the wheel is sufficiently large with respect to the curb,this transfer of energy is relatively smooth and effective. However, asthe radius of the wheel approaches the height of the curb, the energytransfer becomes less effective, until the wheel fails to climbobstacles that exceed its radius.

Currently there is no mechanism that provides generally passive supportfor the platform to which it is attached, provides power for movementover surfaces, and can provide movement across a wide variety ofsurfaces, including those found in rough terrain, urban environments,indoors, and disrupted and partially engineered settings.

SUMMARY OF THE INVENTION

Against this backdrop embodiments of the present invention have beendeveloped. One embodiment of the present invention is a platform wheeledapparatus that incorporates a unique intelligent wheel configuration foreach wheel in which each wheel can dynamically change its radius tonegotiate various obstacles. The intelligent wheel has a rotational hubpreferably fastened to a support disc that carries a series ofextendable, weight bearing spoke mechanisms spaced around the hub thatcan be controllably extended and retracted radially in response to theanticipated terrain surface over which the wheel is to travel. The hubof the wheeled platform wheel carries a microcontroller, positionsensors, preferably a set of obstacle proximity sensors and forcesensors, and an appropriate electrical power supply for operation of thespoke mechanisms and control components.

The hub functions as the mounting point for the intelligent wheel and,in one embodiment, a disc fastened to the hub provides structuralsupport for the other components such as each retractable spokemechanism including a proximity sensor, distance sensor, and forcedetector for each spoke. The central portion of the hub is preferablymechanically connected to a driven axle to provide rotational drivingforce for the platform vehicle. In addition to the mechanical coupling,the central portion of the hub may optionally provide an electricalconnection from a power source mounted on the vehicle platform to supplyelectrical power to the hub mounted electrical components. In theintelligent wheel in accordance with an embodiment of the presentinvention, the spokes are active. These active spokes extend and retractin response to force, distance and position signals from the varioussensors associated with each spoke mechanism. These spoke mechanisms arecontrolled by an automated microprocessor or microcontroller controlsystem that may be mounted on the wheel itself or the vehicle platform.This allows the wheel to adapt to and negotiate over obstacles and voidsin the surface over which it is traveling.

These and other features, advantages and objects of the invention willbecome more apparent from a reading of the following detaileddescription when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of a wheel in accordancewith the present invention with all spokes extended for illustrationpurposes.

FIG. 2 is a simplified representative side view of the wheel shown inFIG. 1.

FIG. 3 is a separate perspective view of one exemplary spoke mechanismfor the wheel shown in FIG. 1.

FIG. 4 is an enlarged partial side view of one of the spoke mechanismsmounted on the wheel shown in FIG. 1.

FIG. 5 is a block diagram of the controller for the wheel in accordancewith the present invention.

FIG. 6 is a schematic operational representation of a wheel inaccordance with an embodiment of the present invention.

FIG. 7 is a representation of the wheel shown in FIG. 6 as it approachesa step.

FIG. 8 is a representation of the wheel shown in FIG. 6 after havingmounted the step shown in FIG. 7.

FIG. 9 is a schematic operational representation of a wheel as in FIG. 6as the wheel approaches a down step.

FIG. 10 is an operational flow control diagram for the controller whenit is controlling positioning of a weight-bearing spoke at bottom deadcenter.

FIG. 11 is an operational flow control diagram for the controller whenit is controlling positioning of a spoke that is approaching bottom deadcenter.

DETAILED DESCRIPTION OF THE INVENTION

An intelligent wheel 100 in accordance with one embodiment of thepresent invention is shown in FIGS. 1-9. Referring now to FIG. 1, thiswheel 100 has a generally disc shaped support portion 102, a central hub104 about the center of the support portion 102, and a series of radialspoke mechanisms 106 fastened to the support portion 102 and positionedequally spaced around the central hub 104. The spoke mechanisms 106 aredynamically controlled by a controller that controls extension of thespoke or spokes 108 which are supporting the hub 104 at any given timeso as to effectively increase or decrease the wheel radius, thus raisingor lowering the center of mass of the wheel 100 and its load as itapproaches and encounters an obstacle or change in the surface 110on/over which it is traveling. In addition, the adjacent spoke or spokes108, which is/are rotating down toward and onto the obstacle, can beextended, such as is shown in FIG. 7, such that they provide a grippoint for the wheel 100 on the obstacle, in this case, a step.

In the case of an obstacle on top of the travel surface 110, thiscombination of movement translates the rotation of the wheel 100 into anupward vertical force that lifts the wheel 100 up onto/over theobstacle. This sequence is reflected in FIGS. 7 and 8, discussed in moredetail below. Thus the adjustable spokes 108 act in two distinct ways toenable the wheel to climb vertical obstacles: 1) the weight bearingspoke(s) extend to lift the center of the wheel; and 2) the leadingspokes (see leading spokes in FIG. 8) can be extended over the obstaclesuch that the continued rotation of the wheel 100 will cause the spoke108 to act as a lever arm and raise the wheel 100. If the obstacle takesthe form of a void in the surface (either a hole, or a drop off, e.g.,down steps) the spokes 108 work in an analogous way to both support thehub 104, and to lower the wheel 100 onto the new elevation of the travelsurface 110. This sequence is reflected in FIG. 9.

There are three classes of sensors positioned either on each of thespoke mechanisms 106 or spaced around the hub 104. One set detects thepresence of vertical obstacles and voids, i.e., proximity or distancesensors, and the second senses the orientation of the hub 104, so thatthe control system can track which spokes are up, and which are down, atbottom dead center (BDC), and track the angle with respect to BDC ofeach spoke 108. The third class of sensors are force sensors that detectboth inline (along the axis of the spokes 108) and lateral (side forceson the spoke tips) forces on the spokes 108. While in many applicationsit might be possible to use external sensors (sensors mounted on themobility platform), this would require that either data streams orcontrol streams be transmitted from the platform onto the rotatingwheel. To reduce the communications needs, and to reduce the sensor lag,in this embodiment of the present invention, the intelligent wheel 100has dedicated sensors mounted on the hub 104 to provide real-time inputabout voids and vertical obstacles which the current spokes 108 may beapproaching.

Position Sensors

The position sensors can be either simple obstacle detectors (presenceor absence information only), or they can be ranging sensors, whichprovide distance information. Preferably, these are ranging sensors sothat the control system can anticipate the timing of approach of thewheel 100 to the obstacle or discontinuity in travel surface 110accurately. Finally, any of a number of sensor technologies may beutilized, including active infrared, sonar, laser, and/or capacitancesensors in the spoke tips. As long as the sensors are preferably capableof responding to the presence of a vertical obstacle within a distanceof about two radii of the wheel 100, and detect voids directly in frontof one or more lowering spokes, i.e., at least the spoke immediately infront of the spoke at BDC, there is anticipated to be enough informationfor the wheel 100 to react to the changes in terrain.

Angular Orientation Sensors

Orientation sensors give the intelligent wheel control systeminformation about which spokes 108 are pointing down, and which are up.This is needed to reduce excess power consumption caused by unnecessaryextension and retraction of the spokes. Only the spokes which arerotating into support positions need to be adjusted to the appropriateextension. This band of positions, about 120 degrees of rotation, asshown in FIG. 6. Those on the remaining portion of the wheel can be leftalone, thus reducing power consumption. To do this, the wheelcontrollers 500 needs to be able to detect the current orientation ofthe wheel 100, and from that identify the active spokes 108.

Force Sensors

The final class of sensors provide feedback on the forces that eachspoke is currently experiencing. This information is used by theintelligent wheel controller to assess the correct response needed forthe wheel 100 to continue moving. For example, during curb climbing, thelead spoke can be extended over the top of the curb to act as a leverand assist in raising the wheel over the obstacle, as is shown in FIG.8. This will put lateral forces on the spoke 108, which can be detectedand integrated with the lifting forces on the other spokes (e.g. one atBDC) to correctly and smoothly lift the wheel 100 up onto and over thecurb or stair tread.

Microcontroller and Software

Given the data from the sensors, and the ability to extend and retractthe adaptive spokes 108, a control system is needed to tie everythingtogether. The final component of the intelligent wheel 100 is amicrocontroller and its associated software. A block diagram of anexemplary control system 500 is shown in FIG. 5. There are a number ofrobust microcontrollers which can support both the input data bandwidthfrom the sensors, and the required control signal data streams to thespokes. The primary function of the microcontroller is to detectupcoming vertical discontinuities, and configure the variable geometryto ‘smooth out’ the travel.

The controller system 500 is an active sensor/controller system that canadapt the effective shape of the wheel to conform to the terrain that isbeing traversed in a reactive manner. This system 500 allows the spokes108 of the intelligent wheel 100 to act as levers and lift the wheel 100when traversing obstacles and when climbing and descending stairs. It isalso designed for efficient traversal of smooth surfaces such as roads,floors and sidewalks, which can be reconfigured to provide high tractiontraversal of rough terrain and obstacles.

One of the spoke mechanisms 106 is separately shown in FIG. 3. The spokemechanism 106 includes a stepper drive motor 302 that carries a spoke108 as its lead screw. The spoke 108 has a ball shaped foot 304 made ofa high friction material such as a rubber or resilient plastic material.This foot 304 may also incorporate within it a force sensor. The stepperdrive motor 302 is fastened to a base plate 306 that is in turn fastenedto the support portion 102. The base plate 306 carries three pairs ofposition sensors 308, 310 and 312. Position sensors 308 sense when thespoke 108 is fully retracted. Position sensors 310 sense when the spoke108 is at a mid position, and position sensors 312 sense when the spoke108 is fully extended. Since this embodiment utilizes a stepper motordriven lead screw spoke arrangement, the sensors 308. 310, and 312 mayalternatively be eliminated if reliance in the controller is made solelyon the stepper motor position. The spoke mechanisms 106 are designed toprovide passive physical support of the wheel 100 and the ability toextend and retract to alter the geometry of the wheel 100. The supportis preferably passive (e.g., it does not require the expenditure ofpower to maintain the extension of the spoke) in order to minimize thepower consumption. The present shown embodiment 106 utilizeselectromechanical lead screws for the extension mechanism. However,these could be replaced with hydraulic actuators, pneumatic actuators,or any scheme that does not require power to hold position.

The spoke mechanisms 106, separately schematically shown in FIGS. 3 and4, are equally spaced and mounted around the circumference of the hub104, with the axis of each spoke 108 aligned radially to the center ofthe hub 104. Thus any extension or retraction of the spoke has theeffect of altering the radius of the wheel 100. In a preferredimplementation the extension of the spoke 108 is achieved by rotating alead nut with a stepper motor 302, controlled by the microcontroller.The total extension of the spoke can approach the diameter of the hub,giving the ability to change the wheel radius by over 200%. In such aconfiguration, the opposing spoke assemblies 106 (on opposite surfacesof the circular wheel 100) would necessarily have to be slightly offsetso as not to interfere with each other (occlusion) when both areretracted. This offset can be either offset to either side of the centerof the wheel or may be in different parallel planes along the Z axis ofthe wheel. An advantage of such a configuration is that it would givethe wheel 100 a wider contact surface, or footprint, which can aid wheeland vehicle stability.

The spokes 108 and driver mechanism 302 are mounted to the support disk102 via a pair of intermediate surface plates 402 and 404 shown in FIG.4. Intermediate surface plate 402 allows a small amount of axial(radial) travel resisted by a spring. This is designed to allow theentire spoke 108 and drive motor mechanism 302 to be forced radiallyinwards in response to an axial load, and return to its normal positionwhen the load is removed.

This intermediate surface 402 is in turn mounted to a secondintermediate surface plate 404 which allows a slight lateral ortangential motion in response to a tangential force applied to the spoke108. Again, springs cause a return to the rest position when thetangential force is removed. This final intermediate surface plate 404completes the mechanical components of the spoke mechanism 106 and thebase plate 306 is mounted directly to the support portion 102 of thewheel 100. The forces on these two intermediate plates 402 and 404 aretransmitted to the controller for use in dynamically compensating forvarious motions of the wheel 100. These sensors provide data about thestate of the wheel and its sub-components to the microcontroller. Asingle position sensor can be used to detect the small radial shiftcaused by radially inward force, and two position sensors can be used todetect the small displacement caused by lateral forces on the spoke 108(one for clockwise force, one for anti-clockwise). Alternatively, asingle resilient baseplate, providing a small amount of displacement inresponse to applied forces in either radial or lateral directions couldbe utilized with the same sensors to provide force information to thecontroller.

There are obstacle sensors associated with each spoke 108. A schematicrepresentation of the sensor positioning is shown in FIG. 2. Each spokemechanism 106 has associated with it a proximity sensor that sensesobjects in a directed path 120. These sensors are generally used todetect either positive or negative vertical discontinuities in theregion directly in front of the associated spoke 108. This informationallows the microcontroller to extend the spoke 108 to either providesupport over a void in the surface 110, or to provide lift to climb overa step or curb. Preferably these sensors are active infrared (IR)ranging sensors; however any one of a number of equivalent technologiescan be used. An orientation sensor (not illustrated) is used todetermine which of the spokes 108 are down and which are up. Thisinformation is used to assess which spokes need to extend or retract inorder to overcome the current obstacles in the path of the wheel. Morepreferably, the wheel orientation sensor(s) may be attached directly tothe driven axle to provide angular position of the wheel 100 andtherefore specific orientation of each spoke 108 to the control system500.

The control system 500 is shown in block diagram form in FIG. 5. Thesystem 500 includes a controller 502, an input/output module 504, amicroprocessor 506, a memory 508, and sufficient Input/Output (I/O)lines 510 to support the various position, orientation, force anddirectional sensors and the spoke mechanism motors 302 in the spokemechanisms 106 spaced around the wheel hub 104. In addition, a necessarypower supply 512 may be provided or power could be supplied from thevehicle drive power (not shown). The controller 502 can be eitherhard-coded, such as a Programmable Logic Controller (PLC), or can be anyone of a number of simple programmable controllers.

The wheel 100 in accordance with the illustrated embodiment of theinvention is schematically shown in side view on a travel surface 110 inFIG. 6, and moving in a direction indicated by arrow 600. The controlsystem 500 views the sensors and spoke mechanisms 106 that lie in theshaded zone 602 as being active. This active zone typically extends fromabout horizontal in the direction of travel clockwise through an angleof about 145 to 160 degrees. This angle can be modified to as little asabout 45 degrees in some applications. However, to anticipate obstacleslike stairs, an active zone angle of at least 90 degrees is believed tobe required. The mechanisms 106 in the active zone 602 are continuouslyproviding information to the control system 500. The mechanisms that arein the inactive, or un-shaded zone 604, are retracted and their sensorsdo not provide data to the control system 500.

Traversing level terrain is the default behavior of the wheel 100. Inthis condition, all spokes 108 are retracted and the wheel 100 rotateson the surface 110 as a normal wheel. In the simplified view of FIG. 6,eight spoke mechanisms 106 with associated spokes 108 and sensors areshown. The spoke 108 at bottom dead center, i.e. weight bearing, isdesignated “BDC”. The immediately adjacent spoke mechanism in thedirection of travel 600 is designated BDC−1, and the spoke mechanism 106next adjacent is designated BDC−2. As the wheel 100 is rotated, thisdesignation sequence changes to the next set of spoke mechanisms as theycome within the active zone 602.

The spokes begin in their ‘at rest’ retracted position as in FIG. 6. Asthe wheel rotates, one spoke after another moves into the active zone(those spokes encompassed by approximately 150°) from horizontally infront of the hub, through to about an angle of 60° behind the hub. Theleading spoke sensors first attempt to detect either a positiveobstacle, or an upward lateral force on the spoke 108. On level terrain,neither of these forces are detected. As the spoke rotates to justbefore the vertical position BDC, the axial sensor is scanned for theexpected inward force. When this is detected, the spoke is left in theretracted state, and no further processing is required. This provides awheel geometry that is an efficient minimal radius circle, and power isonly expended on sensors.

Now consider FIGS. 7 and 8. The behavior associated with uneven terrainclimbing is purely reactive. Each wheel 100 attached to the mobilityplatform (not shown) is responsible for sensing the path in front of it,via the sensors associated with each spoke mechanism 106, and reactingto any sensed obstacles by extending or retracting the appropriate spoke108. The sensor field of view is represented by the hatched areas 802shown in FIGS. 8 and 9. The behavior model is similar to that of levelterrain, except that when the wheel approaches an obstacle (say a curbthat must be climbed), the sensors associated with the spoke 108entering the active zone 602 detect the obstacle, in this case surface110 is a set of stair steps 710. Based on the current orientation of thewheel 100 at the time that the obstacle is detected (BDC−2), the controlsystem 500 can estimate the height of the curb, or first step. Usingthis information, the micro-controller 502 begins extending the seriesof spokes 108 from the beginning of the active zone 602 through to thecurrent weight bearing spoke 108. This is the spoke 108 at BDC in FIGS.6 and 7 and 8. Those spokes 108 that are not yet in contact with thesurface 710, i.e. BDC−1 and BDC−2, are sequentially extended as shown totake the weight of the wheel 100 at slightly greater and greater radii,in effect building a virtual surface or ramp 720 that the outercircumference 101 of the wheel 100 will effectively follow on as thewheel lifts itself up to the height needed to transition onto the uppersurface. The center of the wheel 100 will likewise follow a parallelpath to the virtual surface shown. As the spokes rotate out of theactive zone 602, they are retracted to their rest position, ready to beextended again as needed.

Descent, shown in FIG. 9, is basically the reverse of a climb. However,the sensors associated with the load bearing spokes control the changesin geometry. As the spoke 108 swings into the support role at BDC, thesensors will detect a void immediately in front of (or beneath) theleading (BDC−1) spoke 108. This condition causes the micro-controller502 to extend the spoke at BDC−1 until a surface is encountered (usingthe force sensors). Using this information, and data from the spokes 108swinging into position, the micro-controller 502 can calculate aneffective surface that will lower the wheel 100 smoothly onto the newportion of the travel surface 110. In addition, as a spoke 108 becomesload bearing, the microcontroller can begin the process of retractingthe spoke, thus lowering the wheel 100 down onto the anticipated newlevel.

A control flow diagram 1000 for the wheel 100 at BDC+1 is shown in FIG.10. This process is sequentially performed by the control system 500 foreach spoke mechanism 106 as each rotates into a position just after itis weight bearing, i.e., a BDC+1 position. It should be understood thatthe control system 500 is a continuous sense-plan-act reactive system.As such it is continuously monitoring the sensed environment. However,for the purposes of capturing the control flow, an approximate minimumangular displacement “e” (epsilon) is used herein. This epsilon isdependent on the geometry of the wheel 100, and spokes 108, as well asthe speed of the computational system in microprocessor controller 502and the rotational velocity of the platform drive system. Theseimplementation dependent physical quantities will determine thereactivity of the entire system, and this defines the epsilon term. Ingeneral, this control loop should be executed no less frequently than300 times per complete revolution of the wheel 100. Another term that isused is “delta”. The delta term is used to reduce the effects of sensoruncertainty and surface variation on the wheel operation. It isdependent on both the types of sensors and the environments into whichthe wheel 100 is to be deployed. With low noise sensors and clean smoothsurfaces, the delta term can be very small. However, as the uncertaintyof the sensors increases or as the environment becomes more rugged, thedelta term should be made larger to reduce unnecessary changes to thespoke lengths.

Control begins in operation 1002 where the controller 500 enters a drivemode. Control then transfers to operation 1004. In operation 1004 theintelligent wheel 100 drive motor senses axle rotation by apredetermined amount epsilon. When this position change is detectedcontrol transfers to scan operation 1006.

In scan operation 1006, the sensors associated with the mechanism 106 atthe BDC+1 position, the BDC position, and the position immediatelybefore BDC (BDC−1) are scanned and data provided to the microprocessor502. Control then transfers to query operation 1008.

In query operation 1008, the distance data for the spoke mechanisms atBDC+1, BDC, and BDC−1 are compared in order to determine whether thesensed surface 110 is flat. The calculations are as follows:

FLAT(S1, S2, S3) := (abs(S1−S2) < delta) && (abs(S2−S3) < delta) &&(abs(S1−S3) < delta) && (abs(2*S2−S1−S3) < delta)

Where S1 is the spoke at BDC+1 S2 is spoke at BDC S3 is spoke at BDC−1

If the sensed surface is flat, control transfers to query operation1010. On the other hand, if the sensed surface 110 is not flat, controltransfers to query operation 1014.

In query operation 1010, the query is made of the mechanism 106 at BDC−1whether the spoke 108 is extended. If the spoke is not extended, thenthis is the correct spoke position for flat terrain, so control passesback to rotate the wheel 100 another epsilon operation 1004. However,if, for some reason, the spoke is extended, then the spoke mechanism atBDC−1 is retracted in operation 1012. Control then passes back to rotateepsilon operation 1004.

If the sensed surface 110 is not flat and control passes from queryoperation 1008 to query operation 1014, the direction of the slope isdetermined from a comparison of the BDC and BDC−1 signals. If the slopeis positive, or up, control passes to operation 1016. If the slope isnegative, or down, control passes to operation 1018. The slope directioncalculation in operation 1014 is determined from the following:

Slope (S1, S2) := (S1 − S2) < delta => Down (S1 − S2) > delta => Up

-   -   Where S1 is the surface (sensor BDC+1)=cos(theta−32)*reading    -   Where S2 is the surface (sensor BDC)=cos(theta)*reading    -   Where S3 is the surface (sensor BDC−1)=cos(theta)*reading    -   and where “reading” is the raw distance from the sensor and        “theta” is the angular separation between the axis of the BDC        spoke and the point on the surface directly below the center of        rotation of the wheel.

In operation 1016, the “up” virtual surface for the upcoming leg (BDC−1)is calculated according to the formula:VirtualSurface(BDC−1)=(Surface(BDC+1)+Surface(BDC))/2. Control thentransfers to operation 1018 discussed immediately below.

If the slope is down, a new virtual surface calculation is not needed,but a new leg extension calculation is needed. Control transfers tooperation 1018. Here the leg length for the spoke mechanism 106 at BDC−1is calculated by the formula:leglength(BDC−1)=VirtualSurface(BDC−1)+Extension(BDC)

Control then transfers to operation 1020. In operation 1020 the spokemechanism 106 at BDC−1 position is adjusted as appropriate. Control thentransfers back again to rotate epsilon operation 1004 and the processrepeats.

In addition, for the spoke mechanism 106 at BDC position, the controlflow is as shown in FIG. 11. Control flow 1100 applies to any spokemechanism 106 that becomes weight bearing at BDC. Operations again beginin operation 1002 where drive mode is entered. Control then transfers tooperation 1102 where the wheel 100 is rotated by epsilon. Control thentransfers to scan operation 1104. In scan operation 1104 each of thesensor sets for the spoke mechanisms currently at BDC+1, BDC−1 and BDC−2are scanned for their output data signals. Control then transfers tooperation 1106 where a virtual surface at BDC is calculated. Thus thevirtual surface may be viewed as:VirtualSurface(BDC)=SURFACE(BDC+1)−SURFACE(BDC−1).

Control then transfers to operation 1108 which queries whether the BDCsurface is flat. If it is, control transfers back to rotate epsilonoperation 1102. If it is not flat, then control transfers to queryoperation 1110.

In query operation 1110, the determination is made whether the slope iszero, up (positive) or down (negative). In other words, is thediscontinuity in travel surface a rise or fall. If the slope is up,control transfers to query operation 1112. If the slope is zero, i.e.the surface is flat, control transfers to operation 1116. If the slopeis down, control transfers to query operation 1114.

In query operation 1112, the query is made whether the spoke mechanism106 at BDC is extendable, i.e., whether it can be extended further. Ifso, control transfers to operation 1120 where the leg is extended byabout half the distance from the surface to the current tip position.Control then passes to operation 1122.

In query operation 1114, if the slope is down the query is made whetherthe spoke mechanism at BDC is retractable, i.e. whether there is roomfor further retraction of the spoke 108. If so, control passes tooperation 1118 where the leg is retracted again by about half thedistance from the travel surface to the current spoke tip position.Control then passes to operation 1122.

In query operation 1110, if the slope is zero, then control passes tooperation 1116 where a now leg length at BDC is calculated. Control thenpasses to operation 1122.

In operation 1122 the BDC leg is adjusted. This calculation isexemplified by CALCULATELEG( ) in which the NewLength=VirtualSurface(BDC)+(CurrentExtension(BDC)*γ) where γ is afunction of the rotational velocity of the wheel 100 and the extensionvelocity of the spoke 108. The effect is that the BDC length extensionwill reduce the difference between the current extension and the actualsurface in each iteration by about ½ since there are about 300iterations per revolution of the wheel and a much smaller number ofspokes, the actual value depends on the total travel of the spoke, themaximum velocity of the spoke extension/retraction, the radius of thewheel, and the rotational velocity and direction of rotation of thewheel 100.

The value is relatively insensitive to small errors, since thesense-plan-act control loop is running fairly quickly with respect tothe physical wheel movements. Control then returns to rotate epsilonoperation 1102 and the process repeats for the next spoke mechanism atBDC. The virtual surface is essentially preferably a straight line overthe discontinuity tangent to the outer edge 101 of the wheel 100.Correspondingly, the center of the wheel 100 traverses along a pathparallel to the virtual surface 720 shown in FIGS. 7-9.

It will be clear that the present invention is well adapted to attainthe ends and advantages mentioned as well as those inherent therein.While a presently preferred embodiment has been described for purposesof this disclosure, numerous changes may be made which will readilysuggest themselves to those skilled in the art and which are encompassedin the spirit of the invention as set forth in the following claims.

1. An intelligent wheel apparatus comprising: a generally circular wheeldefining an outer circumference and including a hub adapted for rotationabout an axis in a first direction to move the outer circumference ofthe wheel over a travel surface; a controller coupled to the wheel; aplurality of substantially radially extendable spoke mechanisms spacedaround the hub and fastened to the wheel; means for moving a spoke ineach spoke mechanism between an extended position and a retractedposition in response to commands from the controller, wherein a tip ofthe spoke extends beyond the outer circumference of the wheel when thespoke is moved to an extended position; an obstacle sensor associatedwith each spoke mechanism and coupled to the controller, wherein eachobstacle sensor is capable of detecting a discontinuity in the travelsurface within a predetermined field of view; and wherein the controlleroperably calculates a virtual surface over a detected discontinuitywithin the travel surface and commands one or more spoke mechanisms tomove their respective spokes so that the outer circumference of thewheel substantially follows the calculated virtual surface as theintelligent wheel apparatus moves in the first direction.
 2. Theapparatus according to claim 1, wherein axes of the spokes pass througha center of the wheel.
 3. The apparatus according to claim 1, whereinaxes of the spokes are parallel to a radius through a center of thewheel.
 4. The apparatus according to claim 1 wherein the controllercalculates the virtual surface from at least one sensor signalassociated with a spoke mechanism forward of a bottom dead center (BDC)position of the wheel and a sensor signal associated with a spokemechanism at a position after BDC.
 5. The apparatus according to claim 4wherein the spoke mechanism forward of BDC is at a position BDC−1. 6.The apparatus according to claim 5 wherein the controller calculates adistance from the tip of the spoke in the spoke mechanism at positionBDC−1 to the travel surface to determine an extension amount.
 7. Theapparatus according to claim 6 wherein the controller repeatedlycalculates the extension amount for the spoke mechanism at positionBDC−1 until the spoke mechanism reaches BDC.
 8. The apparatus accordingto claim 5 wherein: the spoke mechanism at the position after BDC is ata position BDC+1; a spoke mechanism forward of the position BDC−1 is ata position BDC−2; and the obstacle sensors associated with the spokemechanisms at positions BDC−2, BDC−1, BDC and BDC+1 are activated tosearch for discontinuities within the travel surface, while the obstaclesensors associated with a remaining plurality of spoke mechanisms thatfall outside of the positions BDC−2, BDC−1, BDC and BDC+1 aredeactivated to conserve power.
 9. The apparatus according to claim 8,wherein the spokes for each of the remaining plurality of spokemechanisms that fall outside of the positions BDC−2, BDC−1, BDC andBDC+1 are moved to a retracted position.
 10. The apparatus according toclaim 8, further comprising an angular orientation sensor to determinewhich of the plurality of spoke mechanisms are located at the positionsBDC−2, BDC−1, BDC and BDC+1.
 11. The apparatus according to claim 1wherein the virtual surface is substantially flat.
 12. The apparatusaccording to claim 1, wherein the controller further comprises acontinuous sense-plan-act reactive system controller.
 13. The apparatusaccording to claim 1, wherein the detected discontinuity within thetravel surface comprises one of a positive or negative verticaldiscontinuity.
 14. The apparatus according to claim 13, wherein thedetected discontinuity within the travel surface further comprises astep.
 15. The apparatus according to claim 1, further comprising a forcesensor associated with each spoke mechanism to provide feedback to thecontroller regarding at least one of a lateral force and a lifting forceapplied to each spoke.
 16. An intelligent wheel apparatus capable ofclimbing and descending steps, comprising: a circular wheel defining ahub and an outer circumference adapted for rotation in a firstdirection, wherein the outer circumference of the wheel is adapted tomove over a travel surface; a plurality of substantially radiallyextendable spoke mechanisms spaced around the hub, wherein each spokemechanism includes means for moving a spoke between a retracted positionand an extended position, and wherein a tip of the spoke extends beyondthe outer circumference of the wheel when the spoke is moved to theextended position; an obstacle sensor associated with each spokemechanism to detect a vertical discontinuity in the travel surfaceindicative of a step; and a controller attached to the wheel and coupledto each spoke mechanism and each obstacle sensor to operably calculate avirtual surface over a detected step, wherein the controller commandsone or more spoke mechanisms to move their respective spokes to engagethe step so that the outer circumference of the wheel substantiallyfollows the calculated virtual surface as the intelligent wheelapparatus moves over the step.
 17. The apparatus according to claim 16wherein the virtual surface is substantially flat.
 18. The apparatusaccording to claim 16, further comprising a force sensor associated witheach spoke mechanism to provide feedback to the controller regarding atleast one of a lateral force and a lifting force applied to each spoke.19. The apparatus according to claim 16, further comprising an angularorientation sensor to determine an orientation for each of the pluralityof spoke mechanisms.
 20. An intelligent wheel apparatus comprising: acircular wheel defining a hub and an outer circumference adapted forrotation in a first direction, wherein the outer circumference of thewheel is adapted to move over a travel surface; a plurality ofsubstantially radially extendable spokes spaced around the hub, eachspoke including a tip positioned substantially within the outercircumference of the wheel when the spoke is in a retracted position,wherein extension of the spoke causes the spoke tip to extend beyond theouter circumference of the wheel to effectively increase the radius ofthe wheel, and wherein the plurality of spoke tips are individuallyextendable and are not connected to adjacent spoke tips; an obstaclesensor to detect a vertical discontinuity in the travel surface as thewheel moves over the travel surface; and a controller operably coupledto the obstacle sensor, wherein the controller operably calculates avirtual surface over a detected vertical discontinuity and selectivelyextends one or more spokes so that the outer circumference of the wheelsubstantially follows the calculated virtual surface as the intelligentwheel apparatus moves in the first direction.